John Calhoun’s Behavioral Sink experiment was undoubtedly one of the most discussed during the 1970s. It is still highly relevant today when the effects of overpopulation are discussed. With his “rat utopias”, Calhoun proved that overpopulation is not a problem because it leads to a scarcity of resources – overpopulation is a problem in itself. It results in violence, a rejection of social roles and the eventual breakdown of society.
Calhoun had been creating “rat utopias” since the 1940s, but it was only his “Universe 25” of 1972 that captured both academia and the public’s attention. Four breeding pairs of mice were introduced into a box 100-inches square and 54-feet high. It was a “perfect universe.” The mice were safe from predators and disease and given ample food and water. Calhoun was trying to figure out how the mice would react to it. After about 100 days, the mice started breeding. They doubled in population every 55 days.
Although the mice were in a sort of “mouse heaven,” things soon took a nasty turn. By Day 315, males had stopped defending their territory – there were too many mice to fight against. Random violence broke out between mice for no reason. Female mice would attack their own offspring. Normal social bonds and interactions completely broke down. Procreation screeched to a halt, infant abandonment soared, and mortality climbed. Cannibalism appeared, even though there was more than enough food, and some mice became pansexual, even though there were ample females for each male. As time went on, it seemed that the mice had lost the ability to carry out the complex social interactions that would allow them to procreate. Fertile females closed themselves off from society and males of reproductive age – Calhoun called them the “beautiful ones” – and did nothing but eat, sleep and groom.
This breakdown of society and social roles was named the “Behavioral Sink.” Calhoun believed it came about when there were too many mice and a lack of important social roles for each one to play. By Day 560, population growth ground to a halt. The box had 2,200 mice, although it was able to hold far more. Barely any mice survived past weaning. Calhoun found that even when enough of the population died off so that only an optimal population remained, the mice were not able to return to their natural behavior. Never being a part of normal society themselves, the mice simply did not know what it was; they did not even show the understanding that they were in an abnormal state of affairs. The population of “Universe 25” slowly became extinct.
Many people believed that the behavior of Calhoun’s mice and the Behavioral Sink could be extrapolated to humans. The connection between a breakdown of social bonds and violence was observed by Emile Durkheim in the late 19th century. In traditional societies, where family expectations and religion held sway, people enjoyed strong social bonds and had distinct social roles to fill. However, as they moved to cities, they found they were fighting for a place in society. In exasperation and a state of helplessness, many fell into poverty or turned to crime, violence and even suicide.
The fear of failing to be a productive member of society and fulfilling social roles can also push people, like the “beautiful ones,” into isolating themselves. The infamous Japanese hikikomori are a case in point. They are people who refuse to leave their rooms, sometimes for years at a time. They feel shame for being unable to fulfill familial expectations, find the “right” job or be a productive member of society. These men (and sometimes women) hole themselves up in their rooms and never come out.
However, it is not clear that a high population density necessarily leads to a breakdown of society and social roles. Humans might be able, with our ingenuity and almost unlimited demands, to create social roles for everyone and avoid the Behavioral Sink. Some critics, such as psychologist Jonathan Freedam, suggested that it was not the density of population that overwhelmed the mice but the large number of social interactions they had to deal with. Humans are able to avoid this, even while living in a highly dense area.